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Corresponding author:. Two series of eight beam specimens were constructed, each series having a stirrup spacing distance of and mm. Historically, the design of concrete structures has been developed fulfil mechanical strength criteria; obtaining structures which bearing capacity well appropriate for service load. However, there are an increasing number of environmental problems, depending on the place where the structure is exposed. The same occurs for structures exposed to marine environment and chemical substances in industrial faetones.
Thus, it becomes one of the damages that cause higher costs for maintenance and operation in several constructions sites using such material Helene and Pereira, On the other hand, in The United States there are approximately , bridges, constructed with reinforced concrete, which are still in service but However their resistance will depend as much on the concrete strength as well as on reinforcement strength.
If any one of them is corroded, the structure will be involved as a whole. It affects the shear strength due to diagonal tensile stress in the structure, which is expected to support high concentration of tensile strength next to bearings. Usually, shear strength is provided by stirrups and a considerable loss of strength may cause a brittle and sudden failure.
This differs from the nature of flexure failure, which begins with a gradual steel deformation due to tensile stress and cracks arising simultaneously as large distortions that alert the situation and give the chance to make corrective decisions Nilson, Yoon et al.
Therefore, cracking width must be taken into consideration at durability design of reinforced concrete structures. In other research Vidal et al. They found that reinforced concrete beams rapidly produced the first cracking failures; but those kept at a low growing rate. Recently, Torres-Acosta et al. It was observed that dry environment favors cracking faster than dampening environments. Experimental method. So as to avoid the formation of galvanic piles on the contact points between the longitudinal and shear steel, those points were covered with an insulation tape.
Besides, wire was replaced by nylon strips in order to hold flexure and shear reinforcements. Beams were cured for 7 days with a water sheet inside forms; then beams were unmolded and covered with a curing compound up to 28 days of age. Figure 1. The curing membrane was removed from side faces by using a metallic bristle brush. Dampening the beams is done by employing polyurethane foams which are fixed at the stirrups zone.
These foams are dampened with NaCI solution every three hours during the dampening cycle, in order to avoid the solution evaporation; beams are covered with a plastic film.
Figure 2. Beams damage induction. In order to monitor the beams cracking progress, a load of 5kN was applied in different stages. Figure 3 shows an experimental diagram, indicating the experimental process underwent by the 16 reinforced concrete beams. Experimental diagram. Preliminary results. From Cylinders of x mm, which were exposed under dampening and drying eyeles, a concentration of water-soluble chlorides at 10 mm depth of 0. Figure 4. Figure 5. The theoretical shear strength is proved to be similar to the shear strength obtained from the test.
It is also concluded that stirrups spacing distance did not influence ductility of tested beams. Figure 6. Deflections for shear reinforcement steel.
Control beams failure was caused by shear strength due to diagonal tensile stress. The cracking pattern is shown in Figure 7 , where we can notice the contribution of fixing stirrups every mm that produced major cracking in the tensile zone, due to heavier loads which are similar to the ones causing the shear strength failure. Figure 7. Cracking Pattern for Control Beams.
Discussion and final comments. This indicates that beams with stirrups spacing of mm are most likely to reach an incipient corrosion level depassivation of reinforced steel , in comparison to mm spacing distance ones. The tested control beams showed that the ultimate shear strength is similar to theoretical strength as per ACI As expected, the beams which were heavily shear reinforced spacing of mm , showed higher ductility capacity.
American Society for Testing and Materials, , Philadelphia. American Society for Testing and Materials, Philadelphia. Jason Weiss y Surendra P. Introduction Historically, the design of concrete structures has been developed fulfil mechanical strength criteria; obtaining structures which bearing capacity well appropriate for service load. Experimental method 2. Beams damage induction 2.
Experimental diagram 3. Deflections for shear reinforcement steel Control beams failure was caused by shear strength due to diagonal tensile stress. Como citar este artigo.
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